Particulate matter filters are increasingly used in automotive emissions systems for reducing particulate concentrations in engine exhaust. When soot accumulates to a threshold level on the particulate filter, a filter regeneration process may be used to burn off the accumulated soot under controlled engine operating conditions. However, over time, such particulates filters can suffer irreversible decreases in trapping efficiencies as the filter degrades (cracks, for example) due to uncontrolled temperature excursion during the filter regeneration process. Losses in trapping efficiency of the particulate filter may result in increased particulate matter emissions well above the regulated limit.
Increasingly stringent particulate matter emissions standards and proposed government-mandated on-board diagnostic (OBD) requirements for monitoring the trapping efficiency of a particulate filter have stimulated much research into new techniques for monitoring particulate filter performance. One method includes determining a pressure differential across a particulate filter. If the pressure differential is less than a threshold pressure differential, then the particulate filter may be leaking. However, this method may not be suitable for detecting a degradation of the filter due to interference effects from ash loading on the filter. Other methods to determine particulate filter leakage include utilizing a soot sensor, located downstream of a particulate filter, to monitor a soot load in exhaust flow and signaling when the soot load exceeds a soot threshold (e.g., the soot threshold may be based on a threshold amount of acceptable soot leakage based on particulate matter emissions). These sensors utilize spatially separated electrodes, which may become electrically connected in response to the soot load exceeding the soot threshold.
However, the inventors herein have recognized potential issues with such systems. As one example, the soot sensor may have low sensitivity to leaked soot due to a relatively small portion of soot being deposited across the electrodes. This may be due to an exhaust pipe geometry and/or poor mixing of soot with the exhaust gas. Furthermore, large diesel particulates and/or water droplets may impinge onto surfaces of the soot sensor, altering the soot sensor reading. Additionally, sensor may have poor repeatability due to erratic exhaust gas flow across the surface of the electrodes. Sensors may also redirect exhaust gas, which may result in a flow rate change across the surface of the electrodes. Both factors may lead to portions of the sensor receiving a greater amount of soot than others. Furthermore, soot sensors may comprise a guide plate for uniformly flowing exhaust gas across a surface of the electrodes. However, the guide plates may introduce packaging restraints and increased manufacturing costs.
In one example, the issues described above may be addressed by a method diverting exhaust gas from an exhaust pipe to a parallel exhaust pathway outside the exhaust pipe, where the exhaust pathway includes rotatable plates coupled to a filtering material in a fixed housing. The method further includes adjusting engine operation based on a rotational speed of the plates. In this way, compensation for particulate filter operation in the exhaust pipe may be controlled with or without electrodes.
As one example, the plates may be configured similar to a paddle-wheel in shape and structure, where the plates rotate as exhaust gas flows through the housing. The filtering material coupleable to the plates is configured to capture soot from the exhaust gas. As the soot accumulates, the plates may rotate faster for a given engine load (e.g., plates with more accumulated soot rotate faster than plates with less soot during identical engine operating conditions), which may indicate that the particulate filter in the exhaust pipe is fully loaded with soot. This indication may signal a regeneration of the particulate filter. As the number of regenerations of the particulate filter increases, the particulate filter may become degraded, which may decrease an ability of the particulate filter to capture soot. As a result, more soot may flow through the particulate filter to the soot sensor, where the plates may become loaded with soot more rapidly than when the particulate filter is not degraded. As such, degradation of the particulate filter in the exhaust conduit may be indicated once a time interval between subsequent regenerations of the filter plates decreases to a time interval less than a threshold time interval.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.